T arm

Transfer RNA

The T-arm or T-loop is a specialized region on the tRNA molecule which acts as a special recognition site for the ribosome to form a tRNA-ribosome complex during protein biosynthesis or translation (biology).

The T-arm has two components to it; the T-stem and the T-loop.

  • The T-stem consists of a series of paired nucleotides, typically 5 pairs, but sometimes as few as 1 or as many as 6.[1][2]
  • The T-loop is also often known as the TΨC arm due to the presence of ribothymidine (T/m5U), pseudouridine and cytidine residues. It folds into a unique structural element consisting of stacked bases in a U-turn, now termed the "T-loop motif".[3]
    • In archaea, the m5U is replaced with N1-methylpseudouridine (m1Ψ). The m5U/m1Ψ modification at position 54 is thought to increase structural stability.[4]

Organisms with T-loop lacking tRNA exhibit a much lower level of aminoacylation and EF-Tu-binding than in organisms which have the native tRNA.[citation needed]

The T-loop motif has been identified as a ubiquitous structural element in a number of noncoding RNAs.[3] At least one other instance of the T-loop, found in rRNA, also carries the m5U modification.[5]

  1. ^ Lang, B. Franz; Lavrov, Dennis; Beck, Natacha; Steinberg, Sergey V. (2012). "Mitochondrial tRNA Structure, Identity, and Evolution of the Genetic Code". In Bullerwell, Charles E. (ed.). Organelle Genetics. Berlin: Springer. pp. 431–474. doi:10.1007/978-3-642-22380-8_17. ISBN 9783642223792.
  2. ^ Dirheimer, G.; Keith, G.; Dumas, P.; Westhof, E. (1995). "Primary, Secondary, and Tertiary Structures of tRNAs". In Söll, Dieter; RajBhandary, Uttam (eds.). tRNA: Structure, Biosynthesis, and Function. Washington, D.C.: ASM Press. pp. 93–126. doi:10.1128/9781555818333.ch8. ISBN 9781555810733.
  3. ^ a b Chan, CW; Chetnani, B; Mondragón, A (September 2013). "Structure and function of the T-loop structural motif in noncoding RNAs". Wiley Interdisciplinary Reviews. RNA. 4 (5): 507–22. doi:10.1002/wrna.1175. PMC 3748142. PMID 23754657.
  4. ^ Wurm JP, Griese M, Bahr U, Held M, Heckel A, Karas M, et al. (March 2012). "Identification of the enzyme responsible for N1-methylation of pseudouridine 54 in archaeal tRNAs". RNA. 18 (3): 412–420. doi:10.1261/rna.028498.111. PMC 3285930. PMID 22274954. In contrast, in most archaea this position is occupied by another hypermodified nucleotide: the isosteric N1-methylated pseudouridine
  5. ^ Powell, CA; Minczuk, M (April 2020). "TRMT2B is responsible for both tRNA and rRNA m(5)U-methylation in human mitochondria". RNA Biology. 17 (4): 451–462. doi:10.1080/15476286.2020.1712544. PMC 7237155. PMID 31948311.